BEHAVIOR OF CCELENTERATA 225 



effect. In Aiptasia annulata the tentacles no longer carry pellets of 

 paper to the mouth, but bend backward along the column and drop 

 them. In the Stoichactis that is'not very hungry such indifferent bodies 

 are removed by the rejecting reaction described on page 202. 



As the sea anemones become still less hungry the reaction to even 

 such food bodies as pieces of crab meat becomes changed. The reaction 

 gradually becomes slower and less precise. In a hungry specimen of 

 Aiptasia the food reaction is rapid, often requiring but ten or fifteen 

 seconds. But after several pieces of meat have been taken, the reaction 

 occupies a much longer period. The tentacles touched by the food may 

 not react for several seconds, then they bend in a languid way toward 

 the centre of the disk, while the adjacent tentacles may not react at all. 

 The food body is not placed so accurately on the mouth as before. At 

 a later stage food applied to the tentacles induces no reaction at all, or 

 a withdrawal of the tentacles, while if it is applied directly to the mouth 

 it is very slowly swallowed. In Stoichactis at this stage food is often 

 carried toward the mouth, then after or even before it reaches the mouth 

 the reaction is reversed and the food is rejected. If two pieces of meat 

 are applied at once to the disk of Stoichactis when in this condition, one 

 may be swallowed while the other is rejected. Often in Aiptasia one 

 piece may be rejected, while the immediately following piece is swal- 

 lowed. The animal seems in a condition of most unstable equilibrium, 

 so that the reactions are most inconstant and variable. No one could 

 suppose, in studying the behavior of a sea anemone in this condition, 

 that the behavior of such organisms is made up of invariable reflexes, 

 always occurring in the same way under the same external conditions. 



As the animal becomes satiated, the food reaction ceases completely. 

 Pieces of crab meat placed on the disk of a Stoichactis in this state are 

 removed by the rejecting reaction already described. Aiptasia either 

 does not react at all when food is applied to the tentacles, or the ten- 

 tacles contract and bend backward — a negative reaction. 



Some anemones are exceedingly voracious, seeming to take food as 

 long as it is mechanically possible for them to do so. This seems to 

 be the case, for example, with Metridium, where the changes in reaction 

 as the animal becomes filled with food are almost lacking. It may feed 

 till the body cavity becomes so completely filled as to cause disturbance 

 of function. As a result the entire mass of food is sometimes disgorged 

 undigested. After this has occurred, Metridium will often take food as 

 before. But in most sea anemones the taking of food ceases before any 

 such disturbance has been produced. 



The rejection of food is not determined merely by the mechanical 

 fulness of the digestive cavity, but is evidently due to the effects of food 



Q 



